maybe you die young so you don’t get your descendants sick
I’ve always wondered why evolution didn’t select for longer lifespans more strongly. Like, surely a mouse that lives twice as long would have more kids and better knowledge of safe food sources. (And lead their descendants to the same food sources.) I have googled for an explanation a few times but not found one yet.
I thought of a potential explanation the other day. The older you get, the more pathogens you take on. (Especially if you’re a mouse.) If you share a den with your grandkids then you might be killing them. Also, if several generations live together, then endemic pathogens stick with the clan much longer. This might eventually wipe out your clan if one of the viruses etc has a bad mutation.
If you die before your offspring even hatch then you might not pass them any pathogens. Especially if you swim a mile up a river that’s dry 90% of the year. https://youtube.com/watch?v=63Xs3Hi-2OU This is very funny and 1 minute long.
Most birds leave the nest (yes?) so perhaps that’s why there’s so many long-lived birds.
Although IIRC, bats live a really long time and have a mountain of pathogens.
Anybody know if this explanation is fleshed out somewhere, or know a better explanation?
a popular theory of aging is the mitochrondial theory of aging.
There are several variants of this theory some of which are definitely false, while some are plausibly in sorta-the-direction. It’s a big controversy and I’m not an expert yada yada yada. Let me assume something like the following is true: aging is a metabolic phenomena where mitochrondia degrade overtime and at some point start to leak damaging byproducts which is substantially responsible for aging. Mitochrondial DNA have less repair mechanism than nuclear DNA. Over time they accrue mutations that are bad (much quicker than nuclear dna).
Species that reproduce fast & many may select less on (mitochrondial) mutational load since its matter less. On the other hand, species that have more selection on mitochrondial mutational load for whatever reason are less fecund. E.g. fetuses may be spontaneously aborted if the mitochrondia have too many mutations.
Some pieces of evidence: eggs contain the mitochrondia and are ‘kept on ice’, i.e. they do not metabolize. Birds have a much stronger selection pressure for high-functioning metabolism (because of flight)[1] and plausibly ‘better mitochrondia’.
[there are also variant-hypotheses possible that have a similar mutation meltdown story but don’t go through mitochrondia per se. There is some evidence and counterevidence for epigenetic and non-mitochrondial mutational meltdown theories of againg too. So not implausible]
My cached mental explanation from undergrad when I was learning about the details of evolution and thinking about this was something along the lines of a heuristic like:
“Many plants and animals seem to have been selected for dying after a successful reproduction event. Part of this may be about giving maximal resources to that reproduction event (maybe your only one, or just your last one). But for animals that routinely survive their last reproductive event, and survive raising the children until the children become independent, then there’s probably some other explanation. I think about this with mice as my prototypical example a lot, since they seem to have this pattern. Commonly both male and female mice will survive reproduction, potentially even multiple cycles. However, mice do seem to be selected for relatively fast senescence. What might underlie this?
My guess is that senescence can cause you to get out of the way of your existing offspring. Avoiding being a drag on them. There are many compatible (potentially co-occurring) ways this could happen. Some that I can think of off the top of my head are:
Not being a vector for disease, while in a relatively weakened state of old age
Not feeding predators, which could then increase in population and put further stress on the population of your descendants / relatives.
Not consuming resources which might otherwise be more available to your descendants / relatives including:
Thanks for the cached explanation, this is similar to what I thought before a few days ago. But now I’m thinking that an older-but-still-youthful mouse would be better at avoiding predators and could be just as fertile, if mice were long lived. So the food & shelter might be “better spent” on them, in terms of total expected descendants. This would only leave the disease explanation, yes?
My understanding was the typical explanation was antagonistic pleiotropy, but I don’t know whether that’s the consensus view.
This seems to have the name ‘pathogen control hypothesis’ in the literature—see review. I think it has all the hallmarks of a good predictive hypothesis, but I’d really want to see some simulations of which parameter scenarios induce selection this way.
They keywords are much appreciated. That second link is only from 2022! I wonder if anybody suggested this in like 1900. Edit: some of the citations are from very long ago
maybe you die young so you don’t get your descendants sick
I’ve always wondered why evolution didn’t select for longer lifespans more strongly. Like, surely a mouse that lives twice as long would have more kids and better knowledge of safe food sources. (And lead their descendants to the same food sources.) I have googled for an explanation a few times but not found one yet.
I thought of a potential explanation the other day. The older you get, the more pathogens you take on. (Especially if you’re a mouse.) If you share a den with your grandkids then you might be killing them. Also, if several generations live together, then endemic pathogens stick with the clan much longer. This might eventually wipe out your clan if one of the viruses etc has a bad mutation.
If you die before your offspring even hatch then you might not pass them any pathogens. Especially if you swim a mile up a river that’s dry 90% of the year. https://youtube.com/watch?v=63Xs3Hi-2OU This is very funny and 1 minute long.
Most birds leave the nest (yes?) so perhaps that’s why there’s so many long-lived birds.
Although IIRC, bats live a really long time and have a mountain of pathogens.
Anybody know if this explanation is fleshed out somewhere, or know a better explanation?
I like this.
Another explanation I have heard:
a popular theory of aging is the mitochrondial theory of aging.
There are several variants of this theory some of which are definitely false, while some are plausibly in sorta-the-direction. It’s a big controversy and I’m not an expert yada yada yada. Let me assume something like the following is true: aging is a metabolic phenomena where mitochrondia degrade overtime and at some point start to leak damaging byproducts which is substantially responsible for aging. Mitochrondial DNA have less repair mechanism than nuclear DNA. Over time they accrue mutations that are bad (much quicker than nuclear dna).
Species that reproduce fast & many may select less on (mitochrondial) mutational load since its matter less. On the other hand, species that have more selection on mitochrondial mutational load for whatever reason are less fecund. E.g. fetuses may be spontaneously aborted if the mitochrondia have too many mutations.
Some pieces of evidence: eggs contain the mitochrondia and are ‘kept on ice’, i.e. they do not metabolize. Birds have a much stronger selection pressure for high-functioning metabolism (because of flight)[1] and plausibly ‘better mitochrondia’.
[there are also variant-hypotheses possible that have a similar mutation meltdown story but don’t go through mitochrondia per se. There is some evidence and counterevidence for epigenetic and non-mitochrondial mutational meltdown theories of againg too. So not implausible]
compare bats? what about their lifespans?
My cached mental explanation from undergrad when I was learning about the details of evolution and thinking about this was something along the lines of a heuristic like:
“Many plants and animals seem to have been selected for dying after a successful reproduction event. Part of this may be about giving maximal resources to that reproduction event (maybe your only one, or just your last one). But for animals that routinely survive their last reproductive event, and survive raising the children until the children become independent, then there’s probably some other explanation. I think about this with mice as my prototypical example a lot, since they seem to have this pattern. Commonly both male and female mice will survive reproduction, potentially even multiple cycles. However, mice do seem to be selected for relatively fast senescence. What might underlie this?
My guess is that senescence can cause you to get out of the way of your existing offspring. Avoiding being a drag on them. There are many compatible (potentially co-occurring) ways this could happen. Some that I can think of off the top of my head are:
Not being a vector for disease, while in a relatively weakened state of old age
Not feeding predators, which could then increase in population and put further stress on the population of your descendants / relatives.
Not consuming resources which might otherwise be more available to your descendants / relatives including:
food
good shelter locations
potential mating opportunities
etc
”
Thanks for the cached explanation, this is similar to what I thought before a few days ago. But now I’m thinking that an older-but-still-youthful mouse would be better at avoiding predators and could be just as fertile, if mice were long lived. So the food & shelter might be “better spent” on them, in terms of total expected descendants. This would only leave the disease explanation, yes?
My understanding was the typical explanation was antagonistic pleiotropy, but I don’t know whether that’s the consensus view.
This seems to have the name ‘pathogen control hypothesis’ in the literature—see review. I think it has all the hallmarks of a good predictive hypothesis, but I’d really want to see some simulations of which parameter scenarios induce selection this way.
They keywords are much appreciated. That second link is only from 2022! I wonder if anybody suggested this in like 1900. Edit: some of the citations are from very long ago